A gyroscope is a sensor that measures angular velocity about a sensitive axis. An ideal yaw gyroscope is sensitive to angular velocity about the Z-axis, which is normal to a plane of the sensor. Ideal pitch and roll gyroscopes are sensitive to angular velocities about the X-axis and the Y-axis which are orthogonal in the plane of the sensor. Ideally, all three gyroscope sensitive axes are mutually orthogonal.
Fabrication imperfections can cause the sensitive axis to deviate from the ideal input axis. For example a yaw gyroscope, which responds to angular velocity about the Z-axis, can also respond to angular velocity about the X-axis and/or the Y-axis.
Cross-axis sensitivity is a measure of the gyroscope sensitivity to angular velocity about an axis orthogonal to the intended input axes. Cross-axis sensitivity causes errors in a system using a gyroscope because the gyroscope responds to angular velocity about an axis other than the intended axis. For example, if the yaw gyroscope has cross-axis sensitivity, it would be responsive to the angular velocity around the X-axis and/or the Y-axis. Hence, the output of the yaw gyroscope would show a response as if there is a Z axis angular velocity although the actual angular velocity is around the X-axis and/or the Y-axis. Correcting the errors caused by cross-axis sensitivity requires calibration of each gyroscope, which is costly.
MEMS gyroscopes are typically fabricated from silicon. The silicon layer is etched using deep reactive ion etching (DRIE). The gyroscopes are formed using batch fabrication, which means several thousand gyroscopes are formed in the single etch step. Gyroscopes using conventional springs are more responsive to the cross-axis sensitivity because conventional springs couple in-plane motion to out-of-plane motion due to fabrication errors. The challenge is to produce a high accuracy gyroscope with high yield and small size to maintain low cost. The present invention addresses such a need.